Introduction

OS / Compiler	GCC 13	GCC 14	GCC 15	Clang 14	Clang 15	Clang 17
Ubuntu 22.04
Ubuntu 24.04
macOS
Windows

H5CPP compiler is an LLVM/Clang–powered reverse schema compiler. Instead of forcing you to design schemas up front, the H5CPP compiler dives into your existing C and C++ code, extracts full type graphs, and automatically generates persistence descriptors. Born out of the H5CPP header-only library, the compiler eliminates the grind of hand-crafting shim code for HDF5 compound datatypes. Mark a variable with a persistence operator (like h5::write), and the H5CPP compiler will walk the AST, discover every dependent type, and in clean topological order emit a ready-to-use header with HDF5 descriptors. Self-contained, include-guarded, and built to drop straight into your workflow.

The payoff? Non-intrusive, reflection-driven persistence for modern C and C++ — the ease of Python or Java–style serialization, but with the raw performance, type safety, and zero-overhead ethos that C and C++ demand. Complex POD structs? Deeply nested arrays? STL containers? No problem. The H5CPP compiler handles them with ease. Today it supports std::vector, tomorrow an ever-growing slice of the STL universe.

std::vector<sn::example::Record> vec 
    = h5::utils::get_test_data<sn::example::Record>(20);

// mark vec with an h5:: operator and delegate 
// the details to h5cpp compiler
h5::write(fd, "orm/partial/vector one_shot", vec );
````

### Example Structs

```cpp
namespace sn {
    namespace typecheck {
        struct Record {
            char  _char; unsigned char _uchar; short _short; unsigned short _ushort;
            int _int; unsigned int _uint; long _long; unsigned long _ulong;
            long long int _llong; unsigned long long _ullong;
            float _float; double _double; long double _ldouble;
            bool _bool;
            // wide characters are not supported in HDF5
            // wchar_t _wchar; char16_t _wchar16; char32_t _wchar32;
        };
    }

    namespace other {
        struct Record {
            MyUInt idx;
            MyUInt aa;
            double field_02[3];
            typecheck::Record field_03[4];
        };
    }

    namespace example {
        struct Record {
            MyUInt idx;
            float field_02[7];
            sn::other::Record field_03[5];
            sn::other::Record field_04[5]; // optimized out, same as previous
            other::Record field_05[3][8];  // array of arrays
        };
    }

    namespace not_supported_yet {
        // NON POD: not supported in phase 1
        struct Container {
            double idx;
            std::string field_05;                  // non-POD
            std::vector<example::Record> field_02; // non-POD
        };
    }

    /* BEGIN IGNORED STRUCT */
    // These structs are not referenced with h5::read|h5::write|h5::create
    struct IgnoredRecord {
        signed long int idx;
        float field_0n;
    };
    /* END IGNORED STRUCT */
}